The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
Magnesium (Mg) is one of the lightest commercially available structure materials. Mg has a density of 1.74 g/cm3 at 20° C., and this characteristic makes it as a promising candidate for structure applications, such as automotive, aircraft, aerospace, and 3C (computer, communication, and consumer electronic product) industries. However, the room temperature formability of magnesium alloys is generally not high, and this has restricted their large-scale application.
Alloying can improve the ductility and formability of Mg alloys. For example, the applicant's co-pending provisional patent application relates to magnesium-zinc based alloys in which the addition of small amounts of calcium or rare earth metals to magnesium-zinc based alloys improve the ductility and formability of sheets formed from these alloys. Nonetheless, the addition of small amount of alloying elements does not effectively strengthen the resulting alloy sheets. It is therefore desirable to further enhance the strength of sheets formed from this type of magnesium alloy.
The inventors are aware of a number of publications that report that high strength magnesium alloys can be formed using a high concentration of alloying elements, in most cases close to or more than 10 wt %. These alloys often include a large amount of zinc, or one or more rare earth elements such as gadolinium, yttrium, neodymium, and cerium. The inclusion of these alloying elements results in precipitation hardening of the Mg-alloy following an ageing treatment through the generation of a multitude of strengthening precipitates, and thus improvement in the strength of these concentrated Mg alloys. In comparison, magnesium alloys with dilute alloying compositions (<3 wt % total alloying composition) have traditionally not been considered to have a similar age-hardening response. The low alloying composition is thought to not be sufficient to produce the requisite strengthening precipitates. Accordingly, such dilute magnesium alloys and sheets made therefrom are not expected to have any significant age-hardening response.
It would therefore be desirable to provide a method of producing a high strength magnesium alloy sheet formed from a dilute magnesium alloy.